There is no real question there.. BO has no where near the strain on a system as wp has. No way could you run as many WP blogs on a single server as you can run blogs using BO. Add to that you can even run more blogs off the server.
BO can generate it's own blogs which is how I use it, or it can manage WP blogs, blogger, blogs or whatever. IMO it'sd a waste to use it to manage WP blogs because you are defeating the purpose of the script.
Blogs Organizer